Piezoelectric vibration components are widely used as oscillators or band-pass filters. In a piezoelectric vibration component, a piezoelectric vibrating element is accommodated in a package, and the accommodating space of the package is sealed. This seeks to prevent other elements from coming into contact with the piezoelectric vibrating element, and to improve environmental resistance by sealing the space in which the piezoelectric vibrating element is accommodated.
Patent Document 1 discloses a piezoelectric vibration component illustrated in FIG. 1. For a piezoelectric vibration component 101, a piezoelectric vibrating element 102 is accommodated in a package 103. The package 103 includes a first package member 104 having an upward opening and a flat-shaped second package member 105 fixed so as to close the opening of the first package member 104. The second package member 105 is bonded to an upper surface of the first package member 104 with a metallic bonding layer 106 made of solder or the like disposed therebetween, thereby hermetically sealing the package 103.
The piezoelectric vibrating element 102 includes a piezoelectric plate 107 made of quartz crystal or piezoelectric ceramic. A first excitation electrode 108 is disposed on an upper surface of the piezoelectric plate 107, and a second excitation electrode 109 is disposed on a lower surface thereof. The piezoelectric vibrating element 102 has an end fixed to the first package member 104 by the use of a conductive adhesive 110. That is, the piezoelectric vibrating element 102 is fixed to the first package member 104 in a cantilever fashion.
The above-described piezoelectric vibration component 101 is hermetically sealed. Accordingly, moisture and the like in the air is not allowed to easily enter it, so age degradation of the characteristics of the piezoelectric vibration component 101 can be mitigated.
Typically, for a piezoelectric element such as the piezoelectric vibrating element 102, if moisture in the air is deposited on the surface of the element because of a temperature change or the like, the increase in mass may reduce the Q value of the piezoelectric element or may raise resonant resistance. In particular, when the piezoelectric plate 107 made of a piezoelectric single crystal, such as quartz crystal, is used, a reduction in Q value or a rise in resonant resistance resulting from the above-described increase in mass may tend to occur. Therefore, the characteristics of the piezoelectric vibration component 101 tend to deteriorate, and if they deteriorate significantly, the element's oscillation may be stopped.
Patent Document 2 listed below discloses a piezoelectric vibration component 121 illustrated in FIG. 2. In the piezoelectric vibration component 121, the piezoelectric vibrating element 102 is accommodated in a package member 122. The package member 122 includes a flat-shaped first package member 123 and a metallic cap 125 bonded on the first package member 123 with an insulation adhesive 124 disposed therebetween. A support 126 is disposed on an upper surface of the first package member 123 integrally with or independently of the first package member 123. A terminal electrode 127 is disposed on an upper surface of the support 126. The terminal electrode 127 is coupled to an end of the piezoelectric vibrating element 102 with a conductive adhesive 128 disposed therebetween.
The package 122 for piezoelectric vibration component 121 is sealed. However, the seal is not as effective as that occurring when the metallic bonding layer 106 illustrated in FIG. 1 is used. Accordingly, water in the air may enter the inside of the package from the outside of it. To address this, Patent Document 3 listed below discloses placing a desiccant 129 in an accommodating space of piezoelectric vibration component 121. The desiccant 129 absorbs entering moisture, to suppress condensation on the surface of the piezoelectric vibrating element 102 resulting from a temperature change.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-198741
Patent Document 2: Japanese Unexamined Patent Application Publication No. 9-36691
Patent Document 3: Japanese Unexamined Patent Application Publication No. 6-314928